Small nitpick, it's not just the variation in area that you'd care about, but the variation in shape. Two pieces of the same area/volume can cook very differently depending on the shape. The thing is, there isn't a single canonical metric for measuring shape similarity afaik, but you could pick something e.g. based on Hausdorff distance https://en.wikipedia.org/wiki/Hausdorff_distance#Definition A quick search leads to some cool papers https://webspace.science.uu.nl/~veltk101/publications/art/sm...

Bringing Hausdorff distance into a discussion about onion slicing. Love it.